Bupropion hydrochloride produces conditioned hyperactivity in rats

Understanding the stimulus effects of nicotine and bupropion in a drug-drug discriminated goal-tracking task

RATIONALE

Bupropion is a non-nicotine medication for smoking cessation that has overlapping stimulus effects with nicotine as demonstrated in drug discrimination studies. Whether these shared stimulus effects will alter acquisition or maintenance of a discrimination between nicotine and bupropion is unknown.

OBJECTIVE

We sought to test this possibility using the drug discriminated goal-tracking (DGT) task and whether discrimination training history affected generalization and substitution tests.

METHODS

Sixty adult Sprague-Dawley rats (30M/30F) were equally split into three discrimination training groups: SAL-0.4NIC, 10BUP-0.4NIC, and 20BUP-0.4NIC. On nicotine days, all rats were administered subcutaneously 0.4 mg/kg nicotine and had intermittent access to liquid sucrose. On intermixed non-reinforced days, rats were administered intraperitoneally saline, 10 or 20 mg/kg bupropion. Upon completion, a range of nicotine and bupropion doses were assessed before substitution tests with varenicline and sazetidine-A were conducted.

RESULTS

The SAL-0.4NIC and 10BUP-0.4NIC groups readily discriminated by session 8, as evidenced by increased dipper entries (goal-tracking) on nicotine days. The 20BUP-0.4NIC group was slower to acquire the discrimination. Female rats, regardless of group, had higher conditioned responding evoked by the lowest dose of nicotine (0.025 mg/kg) in the dose-effect curve. The discrimination required rats to learn to withhold responding to the training dose of bupropion. This withholding of excitatory dipper entries generalized to other doses. Varenicline and sazetidine-A partially substituted for the nicotine stimulus, and this pattern did not differ with training history.

CONCLUSIONS

We are the first to study a drug-drug discrimination using the DGT task. Females appeared to have a lower discrimination threshold for nicotine that was not impacted by the learning history. Further work on the importance of sex as a biological variable and how the complex interoceptive stimulus effects of nicotine can vary with training histories is needed.

Exposure to dilute concentrations of bupropion affects zebrafish early life stages

Psychiatric pharmaceuticals are one of the most prescribed active substances globally. Bupropion (BPP) is an antidepressant that acts via inhibition of norepinephrine and dopamine reuptake. It has been found in various water matrices, and thus its effects on aquatic organisms must be studied. The present study aimed to evaluate the acute toxic effects of BPP on zebrafish (Danio rerio) early life stages. For developmental analysis, organisms were exposed for 168 h to concentrations ranging from 0 to 82000 μg/L. Two other experiments were performed by exposing embryos to a wide range of concentrations (from 0 to 50000 μg/L) in order to evaluate BPP effects on embryonic behavior, using the Zebrabox and testing at the biochemical level (acetylcholinesterase, glutathione-S-transferase, lactate dehydrogenase and catalase). Developmental analysis indicated that BPP had low acute toxicity with a calculated 168 h-LC50 of 50346 μg/L. Concentrations equal to or above 44800 μg/L elicited several effects such as hatching delay, edemas and tail deformities. However, concentrations from 7300 μg/L upwards elicited equilibrium alteration. Behavioral analysis showed that BPP affected zebrafish locomotor behavior by decreasing activity at 0.6 μg/L, increasing activity at 8.8 and 158 μg/L, and decreasing activity at 50000 μg/L. Biochemical analysis showed an increase of AChE activity at 158 and 2812 μg/L, an increase in GST at the highest concentrations, CAT alteration and increase of LDH at 0.6, 2812 and 50000 μg/L. We can conclude that BPP affects zebrafish early life stages at environmental concentrations.

Systematic review of preclinical, clinical, and post-marketing evidence of bupropion misuse potential

Background: Bupropion is a substituted cathinone compound widely used as a first line or add-on treatment for depression, smoking cessation, and more recently in combination with naltrexone for weight loss. As abuse of synthetic cathinone compounds has received more attention in recent years, concern about the misuse potential of bupropion has grown as well. Objectives: We review bupropion pharmacology and assessments of misuse potential including preclinical evidence, human studies, and post-marketing surveillance of bupropion misuse. Methods: This review reports the results of a systematic review of publications evaluating the potential for bupropion to be misused. Publications were identified using PubMed and Medline through Ovid® as well as iterative bibliographic searches. A summary of data from informal sources of information including substance-user experience from online forum entries is included. Results: Preclinical evidence demonstrates some potential for misuse based on psychomotor, discrimination, self-administration, and conditioned place preference tasks. However, this potential is less than that of commonly misused stimulants. Studies in human populations similarly indicate that bupropion shares interoceptive effects with other stimulants, but lacks some key reinforcing effects of other stimulants. In the real-world setting, misuse of bupropion occurs, but is uncommon. Adverse effects of bupropion misuse are frequently cited as significant barriers to obtaining any desired interoceptive effect. Conclusions: While bupropion demonstrates some potential for misuse, pharmacological differences from other structurally-related stimulants limit bupropion's reinforcing effects. Without additional data indicating susceptibility of specific populations to bupropion misuse, there is no empirical data suggesting a need to modify bupropion prescribing patterns.

The effect of N-acetylcysteine or bupropion on methamphetamine self-administration and methamphetamine-triggered reinstatement of female rats

N-acetylcysteine and bupropion are two promising candidate medications for treatment of substance use disorder. The effects of N-acetylcysteine or bupropion on methamphetamine self-administration of female rats are not well understood. To fill this gap, this study assessed the effects of N-acetylcysteine (0, 30, 60, or 120 mg/kg) and bupropion (0, 10, 30, and 60 mg/kg) on methamphetamine self-administration of female rats across the natural estrous cycle. Following a completed dose-response curve, responding for methamphetamine self-administration was extinguished and the effects of N-acetylcysteine or bupropion on methamphetamine-triggered reinstatement was evaluated in separate experiments. N-acetylcysteine did not decrease responding maintained by methamphetamine or methamphetamine-triggered reinstatement. Bupropion significantly decreased methamphetamine self-administration and methamphetamine-triggered reinstatement in female rats with highest dose (60 mg/kg) also significantly decreasing general chamber activity. In a companion experiment, testing the effect of bupropion on responding maintained by sucrose, we confirmed non-specificity of bupropion's effects as bupropion also decreased responding for sucrose. Considered together, our findings suggest that while N-acetylcysteine has considerable promise for treatment of cocaine dependence it may not generalize to other stimulants like methamphetamine. Furthermore, although bupropion has been shown to effectively decrease methamphetamine self-administration, and presently methamphetamine-triggered reinstatement, its locomotor and reward suppressing effects warrant further investigation including both sexes.

Effects of bupropion on the ejaculatory response of male rats

Chronic antidepressant treatment is associated with sexual side effects, particularly affecting the ejaculatory response. Bupropion (BP), an antidepressant inhibiting dopamine/noradrenaline reuptake, seems to have a low impact upon male sexual function. Ejaculation is regulated both at the brain and spinal cord by the spinal generator for ejaculation (SGE). We investigated the effects of chronic BP treatment on ejaculatory behavior and on SGE functioning. Sexually experienced male rats were intraperitoneally (i.p.) injected with BP (7.5 or 15 mg kg(-1)) during 14 days and tested for sexual behavior on days 1, 7 and 14 of treatment; these same males were used to evaluate the functioning of the SGE by recording the genital motor pattern for ejaculation (GMPE). Acute and chronic BP administration did not importantly modify copulatory behavior of male rats. Chronic treatment with the low dose of BP produced deficits in the functioning of the SGE that were restored by activation of the SGE through afferent stimulation. Conversely, chronic treatment with the high-dose of BP disrupted the functioning of the SGE, as the deficits were not compensated by activating the SGE through sensory stimulation. It is concluded that chronic BP at high doses alters the functioning of the SGE.

Bupropion induced changes in exploratory and anxiety-like behaviour in NMRI male mice depends on the age

The aim of this study was to assess the effects of the antidepressant bupropion on anxiety and novelty-seeking in adolescent mice of different ages and adults. Behavioural differences between early adolescent, late adolescent and adult NMRI mice were measured both in the elevated plus-maze and the hole-board tasks following acute administration of bupropion (5, 10, 15, 20mg/kg) or saline. In the plus maze test, early and late adolescent mice treated with bupropion (10, 15mg/kg, respectively) had lower percentages of entries in the open-arms compared to their vehicle controls. Adult mice treated with bupropion did not differ from their vehicle controls. These results suggest that the effect of this drug on anxiety-like behaviour in mice depends on the age, showing adolescents an anxiogenic-like profile. In the hole-board, adolescents showed more elevated levels of novelty-seeking than adults, exhibiting shorter latency to the first head-dip (HD) and a higher number of HD's. Bupropion increases the latency to the first HD and decreases the number of HD's in all age-groups, indicating a decline in exploratory tendency. Findings reveal that the age can modulate the behaviour displayed by mice in both animal models, and that adolescents are more sensitive to bupropion's anxiogenic effects.

Behavioral characterization of the 6-hydroxidopamine model of Parkinson's disease and pharmacological rescuing of non-motor deficits

BACKGROUND

Parkinson's disease (PD) is a chronic neurodegenerative condition that is characterized by motor symptoms as a result of dopaminergic degeneration, particularly in the mesostriatal pathway. However, in recent years, a greater number of clinical studies have focused on the emergence of non-motor symptoms in PD patients, as a consequence of damage on the mesolimbic and mesocortical dopaminergic networks, and on their significant impact on the quality of life of PD patients. Herein, we performed a thorough behavioral analysis including motor, emotional and cognitive dimensions, of the unilateral medial forebrain bundle (MFB) 6-hydroxidopamine (6-OHDA)-lesioned model of PD, and further addressed the impact of pharmacological interventions with levodopa and antidepressants on mood dimensions.

RESULTS

Based on apomorphine-induced turning behaviour and degree of dopaminergic degeneration, animals submitted to MFB lesions were subdivided in complete and incomplete lesion groups. Importantly, this division also translated into a different severity of motor and exploratory impairments and depressive-like symptoms; in contrast, no deficits in anxiety-like and cognitive behaviors were found in MFB-lesioned animals. Subsequently, we found that the exploratory and the anhedonic behavioural alterations of MFB-lesioned rats can be partially improved with the administration of both levodopa or the antidepressant bupropion, but not paroxetine.

CONCLUSIONS

Our results suggest that this model is a relevant tool to study the pathophysiology of motor and non-motor symptoms of PD. In addition, the present data shows that pharmacological interventions modulating dopaminergic transmission are also relevant to revert the non-motor behavioral deficits found in the disease.

Neurophysiology of Nicotine Addiction

Tobacco use is a major health problem, and nicotine is the main addictive component. Nicotine binds to nicotinic acetylcholine receptors (nAChR) to produce its initial effects. The nAChRs subtypes are composed of five subunits that can form in numerous combinations with varied functional and pharmacological characteristics. Diverse psychopharmacological effects contribute to the overall process of nicotine addiction, but two general neural systems are emerging as critical for the initiation and maintenance of tobacco use. Mesocorticolimbic circuitry that includes the dopaminergic pathway originating in the ventral tegmental area and projecting to the nucleus accumbens is recognized as vital for reinforcing behaviors during the initiation of nicotine addiction. In this neural system β2, α4, and α6 are the most important nAChR subunits underlying the rewarding aspects of nicotine and nicotine self-administration. On the other hand, the epithalamic habenular complex and the interpeduncular nucleus, which are connected via the fasciculus retroflexus, are critical contributors regulating nicotine dosing and withdrawal symptoms. In this case, the α5 and β4 nAChR subunits have critical roles in combination with other subunits. In both of these neural systems, particular nAChR subtypes have roles that contribute to the overall nicotine addiction process.

Mechanistic insights into nicotine withdrawal

Smoking is responsible for over 400,000 premature deaths in the United States every year, making it the leading cause of preventable death. In addition, smoking-related illness leads to billions of dollars in healthcare expenditures and lost productivity annually. The public is increasingly aware that successfully abstaining from smoking at any age can add years to one's life and reduce many of the harmful effects of smoking. Although the majority of smokers desire to quit, only a small fraction of attempts to quit are actually successful. The symptoms associated with nicotine withdrawal are a primary deterrent to cessation and they need to be quelled to avoid early relapse. This review will focus on the neuroadaptations caused by chronic nicotine exposure and discuss how those changes lead to a withdrawal syndrome upon smoking cessation. Besides examining how nicotine usurps the endogenous reward system, we will discuss how the habenula is part of a circuit that plays a critical role in the aversive effects of high nicotine doses and nicotine withdrawal. We will also provide an updated summary of the role of various nicotinic receptor subtypes in the mechanisms of withdrawal. This growing knowledge provides mechanistic insights into current and future smoking cessation therapies.

An investigation of bupropion substitution for the interoceptive stimulus effects of nicotine

Although the exact mechanism that makes bupropion hydrochloride (Zyban) effective as a smoking cessation aid has not been fully elucidated, studies have found that bupropion and nicotine share behavioural and neurophysiological properties suggesting that bupropion might serve as a substitute for nicotine. In fact, bupropion prompts nicotine-appropriate responding in operant and Pavlovian drug discrimination studies with rats. A majority of the literature examining this substitution pattern has been done with an operant paradigm. The present research extended this literature by further characterising the behavioural and neuropharmacological properties underlying the substitution for a nicotine conditioned stimulus (CS). Examination of the dose-effect function and temporal dynamics of this substitution pattern showed that bupropion (20 mg/kg) produced conditioned responding similar to nicotine (0.4 mg base/kg) (ED(50) = 9.9 mg/kg) at 15 and 30 min after injection and partially substituted 5 and 60 min post-injection. Bupropion produced a pattern of conditioned responding similar to nicotine during a 60-min extinction test. Additionally, it has been hypothesised that bupropion and nicotine have an overlapping dopaminergic mechanism. We tested the effects of bupropion pretreatment, the nicotine dose-effect function and the ability of dopamine antagonist to block the substitution of bupropion for nicotine. Pretreatment with doses of bupropion that did not substitute for the nicotine stimulus (5 and 10 mg/kg) did not affect nicotine-conditioned responding; pretreatment with 20 mg/kg attenuated nicotine-evoked responding. Pretreatment with the dopamine antagonists SCH-23390 and eticlopride blocked the substitution. Finally, S,S-hydroxybupropion, the major metabolite of bupropion in humans, did not substitute for the nicotine CS.

Bupropion and nicotine enhance responding for nondrug reinforcers via dissociable pharmacological mechanisms in rats

RATIONALE

Nicotine serves as a primary reinforcer but also potently enhances responding for nonnicotine stimuli with reinforcing properties. One of the most successful pharmacotherapies for smoking cessation, bupropion, also increases responding for nondrug reinforcers such as food and brain stimulation rewards.

OBJECTIVE

The present studies investigated whether treatment with bupropion and nicotine had similar effects on responding for a reinforcing visual stimulus (VS). They also investigated whether the effects of bupropion and nicotine depended on common pharmacological substrates.

RESULTS

Nicotine (0.4 mg/kg base) enhanced responding for the VS, and this enhancing effect increased across testing sessions, replicating our previous findings. Bupropion (3, 10, and 30 mg/kg salt) dose-dependently increased responding for the VS. Treatment with 10 and 30 mg/kg bupropion resulted in a profile similar to nicotine; operant responding increased over repeated drug treatments. The reinforcement enhancing effect of nicotine, but not bupropion, was blocked by pretreatment with the nicotinic acetylcholine receptor antagonist mecamylamine. In contrast, the reinforcement enhancing effect of bupropion, but not nicotine, was blocked by pretreatment with the alpha noradrenergic antagonist prazosin.

CONCLUSION

The reinforcement enhancing effects of nicotine and bupropion increased over time and repeated treatments suggesting a shared mechanism of action. However, the reinforcement enhancing effects of nicotine are mediated by nicotinic acetylcholine receptors, whereas the reinforcement enhancing effects of bupropion were mediated by alpha noradrenergic receptors.

Is the inhibition of nicotinic acetylcholine receptors by bupropion involved in its clinical actions?

In this mini review we will focus on those molecular and cellular mechanisms exerted by bupropion (BP), ultimately leading to the antidepressant and anti-nicotinic properties described for this molecule. The main pharmacological mechanism is based on the fact that BP induces the release as well as inhibits the reuptake of neurotransmitters such as a dopamine (DA) and norepinephrine (NE). Additional mechanisms of action have been also determined. For example, BP is a noncompetitive antagonist (NCA) of several nicotinic acetylcholine receptors (AChRs). Based on this evidence, the dual antidepressant and anti-nicotinic activity of BP is currently considered to be mediated by its stimulatory action on the DA and NE systems as well as its inhibitory action on AChRs. Considering the results obtained in the archetypical mouse muscle AChR, a sequential mechanism can be hypothesized to explain the inhibitory action of BP on neuronal AChRs: (1) BP first binds to AChRs in the resting state, decreasing the probability of ion channel opening, (2) the remnant fraction of open ion channels is subsequently decreased by accelerating the desensitization process, and (3), BP interacts with a binding domain located between the serine (position 6') and valine (position 13') rings that is shared with the NCA phencyclidine and other tricyclic antidepressants. This new evidence paves the way for further investigations using AChRs as targets for the action of safer antidepressants and novel anti-addictive compounds.

Nicotine exposure during adolescence induces a depression-like state in adulthood

There is a strong link between tobacco consumption and mood disorders. It has been suggested that afflicted individuals smoke to manage mood, however, there is evidence indicating that tobacco consumption can induce negative mood. This study was designed to investigate whether nicotine exposure during adolescence influences emotionality/behavioral functioning later in life. Adolescent (postnatal days, PD 30-44) male rats were treated with twice-daily injections of nicotine (0, 0.16, 0.32, or 0.64 mg/kg) for 15 consecutive days, and their behavioral reactivity to various behavioral paradigms (the elevated plus maze (EPM), sucrose preference, locomotor activity in the open field, and forced swim test (FST) was assessed 24 h (short term) or 1-month (long term) after exposure. Separate groups of adult rats received nicotine (0.32 mg/kg) to control for age-dependent effects. We report that nicotine exposure during adolescence-but not adulthood-leads to a depression-like state manifested in decreased sensitivity to natural reward (sucrose), and enhanced sensitivity to stress- (FST) and anxiety-eliciting situations (EPM) later in life. Our data show that behavioral dysregulation can emerge 1 week after drug cessation, and that a single day of nicotine exposure during adolescence can be sufficient to precipitate a depression-like state in adulthood. We further demonstrate that these deficits can be normalized by subsequent nicotine (0.32 mg/kg) or antidepressant (ie fluoxetine or bupropion; 10 mg/kg) treatment in adulthood. These data suggest that adolescent exposure to nicotine results in a negative emotional state rendering the organism significantly more vulnerable to the adverse effects of stress. Within this context, our findings, together with others indicating that nicotine exposure during adolescence enhances risk for addiction later in life, could serve as a potential model of comorbidity.

Pavlovian drug discrimination with bupropion as a feature positive occasion setter: substitution by methamphetamine and nicotine, but not cocaine

Bupropion can serve as a discriminative stimulus (S(D)) in an operant drug discrimination task, and a variety of stimulants substitute for the bupropion S(D). There are no reports, however, of bupropion functioning as a Pavlovian occasion setter (i.e. feature positive modulator). The present experiment seeks to fill this gap in the literature by training bupropion in rats as a feature positive modulator that disambiguates when a light will be paired with sucrose. Specifically, on bupropion (10 mg/kg intraperitoneal) sessions, offset of 15-second cue lights were followed by brief delivery of liquid sucrose; saline sessions were similar except no sucrose was available. Rats readily acquired the discrimination with more conditioned responding to the light on bupropion sessions. Bupropion is approved for use as a smoking cessation aid, and more recently has drawn attention as a potential pharmacotherapy for cocaine and methamphetamine abuse. Accordingly, after discrimination training, we tested the ability of cocaine (1-10 mg/kg), methamphetamine (0.1 to 1 mg/kg) and nicotine (0.00625 to 0.2 mg/kg) to substitute for the bupropion feature. Nicotine (0.05 mg/kg) and methamphetamine (0.3 mg/kg) substituted fully for bupropion; cocaine did not substitute. These results extend previous research on shared stimulus properties between bupropion and other stimulants to a Pavlovian occasion setting function. Further, this is the first report of nicotine and methamphetamine substitution for bupropion. The overlap in stimulus properties might explain the effectiveness of bupropion as a smoking cessation aid and highlight the possible utility of bupropion for treatment of stimulant use disorder.

The contribution of the central nucleus of the amygdala to individual differences in amphetamine-induced hyperactivity

Rats classified as high responders (HR) based on their response to an inescapable novel environment self-administer more amphetamine and have greater amphetamine-induced sensitization than rats classified as low responders (LR). Recent research suggests that the central nucleus of the amygdala (ACe) contributes to the elevated self-administration in HR rats. Therefore, the current study examined the role of the ACe in the expression of both amphetamine-induced sensitization and conditioned hyperactivity in HR and LR rats. Male Sprague-Dawley rats were screened for their response to inescapable novelty and classified as HR or LR rats. Rats were implanted with bilateral cannulae into the ACe and received amphetamine (1.0 mg/kg, s.c.) or saline injections immediately prior to 1-h locomotor sessions. Following five training sessions, all rats received an infusion of muscimol (0.5 microg/0.5 microl) or phosphate buffered saline (PBS) followed by a saline injection to measure conditioned hyperactivity. HR rats displayed conditioned hyperactivity, while LR rats did not, suggesting that HR and LR rats differ in the expression of conditioned hyperactivity. While ACe inactivation attenuated the expression of conditioned hyperactivity, it did not differentially affect HR and LR rats. Following additional training and a 10-day rest period, all rats were then tested for amphetamine-induced sensitization (1.0 mg/kg) following an infusion of muscimol or PBS. Inactivation of the ACe attenuated the expression of sensitization only in HR rats. These results suggest the ACe contributes to the greater amphetamine sensitization in HR rats.

Bupropion attenuates methamphetamine self-administration in adult male rats

Bupropion is a promising candidate medication for methamphetamine use disorder. As such, we used a preclinical model of drug-taking to determine the effects of bupropion on the reinforcing effects of methamphetamine (0.025, 0.05 or 0.1 mg/kg/infusion). Specificity was determined by investigating the effects of bupropion on responding maintained by sucrose. In the self-administration study, rats were surgically prepared with indwelling jugular catheters and trained to self-administer methamphetamine under an FR5 schedule. A separate group of rats was trained to press a lever for sucrose. Once responding stabilized, rats were pretreated with bupropion (0, 10, 30 and 60 mg/kg i.p.) 5 min before chamber placement in a unique testing order. Following acute testing, rats were then repeatedly pretreated with 30 and 60 mg/kg bupropion. Acute treatments of bupropion dose dependently reduced drug intake for 0.025-0.1 mg/kg methamphetamine; sucrose deliveries were only reduced with the high bupropion dose. Repeated exposure to 60 mg/kg bupropion before the session resulted in a consistent decrease in methamphetamine intake (0.05 and 0.1 mg/kg) and sucrose deliveries. Considered together, this pattern of findings demonstrates that bupropion decreases responding for methamphetamine, but the effects are only somewhat specific.

Methamphetamine functions as a positive and negative drug feature in a Pavlovian appetitive discrimination task

This research determined the ability of methamphetamine to serve as a positive or negative feature, and assessed the ability of bupropion, cocaine, and naloxone to substitute for the methamphetamine features. Rats received methamphetamine (0.5 mg/kg, intraperitoneally) or saline 15 min before a conditioning session. For the feature positive (FP) group, offset of 15-s cue lights was followed by access to sucrose on methamphetamine sessions; sucrose was withheld during saline sessions. For the feature negative (FN) group, the light offset was followed by sucrose on saline sessions; sucrose was withheld during methamphetamine sessions. During acquisition, the FP group had higher responding on methamphetamine sessions than on saline sessions. For the FN group, responding was higher on saline sessions than on methamphetamine sessions. Conditioned responding was sensitive to methamphetamine dose. For the FP group, bupropion and cocaine fully and partially substituted for methamphetamine, respectively. In contrast, both drugs fully substituted for methamphetamine in the FN group. Naloxone did not substitute in either set of rats. FP-trained rats were more sensitive to the locomotor stimulating effects of the test drugs than FN-trained rats. This research demonstrates that the pharmacological effects of methamphetamine function as a FP or FN in this Pavlovian discrimination task and that training history can affect conditioned responding and locomotor effects evoked by a drug.

A novel approach for predicting antidepressant-induced sexual dysfunction in rats

RATIONALE

Sexual dysfunction is associated with antidepressant discontinuation. Therefore, there is a need for models that predict antidepressant-induced sexual dysfunction.

OBJECTIVE

To develop a predictive method for evaluating antidepressant-induced sexual dysfunction.

METHODS

Male Sprague-Dawley rats were allowed access to sexually receptive females during a single overnight mating session and then treated with antidepressants known to produce differing levels of sexual dysfunction in the clinic. Two to three weeks later, following either acute, subchronic (7-day), or chronic (14-day) antidepressant treatment, rats were observed for penile erections (PE) in the presence of sexually receptive females that were not accessible for contact but served as visual, auditory, and olfactory stimuli in the testing area.

RESULTS

Chronic treatment of fluoxetine (10 mg/kg), desipramine (10 mg/kg), and bupropion (20 mg/kg) reduced the number of PE 71, 53, and 8%, respectively, relative to vehicle-treated rats. This rank order of the compounds' propensity for reducing PE is comparable to the rank order of the compounds' ability to produce sexual dysfunction during antidepressant treatment in the clinic. Additionally, drugs used to treat antidepressant-induced sexual dysfunction in the clinic, such as sildenafil, yohimbine, and dopamine agonists, were also effective in attenuating the deficits in the number of noncontact PE produced by chronic fluoxetine treatment.

CONCLUSIONS

Taken together, this model represents a novel approach for predicting antidepressant-induced sexual dysfunction in rats, which parallels the pattern of reports of sexual dysfunction in the clinic associated with different antidepressant treatments and the ability of adjunct treatment to reverse the sexual impairments produced by antidepressants.